Prediction of the two-dimensional Janus ferrovalley material LaBrI

Two-dimensional (2D) ferrovalley materials, displaying coexistence of spontaneous spin and valley polarizations, have recently attracted significant attention due to their potential for applications in the fields of spintronics and valleytronics. However, unfortunately, to date only a few 2D ferrovalley materials exist. Here, first-principles calculations predict a 2D Janus ferrovalley material lanthanum bromiodide (LaBrI). It is found that LaBrI is a stable ferromagnetic electride, whose magnetic moment originates mainly from the interstitial anionic electrons. The magnetic transition temperature of LaBrI monolayers is estimated to be far beyond room temperature, and a sizable magnetic anisotropy with easy in-plane magnetization is also present. Most importantly, LaBrI monolayers exhibit a large valley polarization due to the concurrent broken space- and time-reversal symmetries, with the calculated valley polarization reaching up to 59 meV. This value is comparable to that of the ferrovalley materials reported to date. Intriguingly, the inequivalent Berry curvature at the two valleys takes opposite values, giving rise to an anomalous valley Hall effect, where a valley current with an accompanying net charge Hall current may be induced.